The present invention relates to an apparatus and method for programming an authentication code, or identification code, to be used between a base station and a mobile station in a communication system. It is an object of the present invention to provide an improved authentication check method and apparatus which renders false signals or manipulation, either intentional or unintentional, less likely. The base station unit provides identification code information to the mobile units without the need for modifying the handset or base. The proposed method and apparatus can also be applied to other mobile communications systems such as paging systems.
There are a variety of communication systems in which one or more mobile units communicate with a central base station unit. Examples of such systems include mobile telephone systems, garage door openers and remote computer terminals. In such systems, each mobile unit must communicate only with one base unit, and similarly, each base unit must communicate only with a specified group of mobile units.
xe2x80x9cCordlessxe2x80x9d telephones include a hand held unit or xe2x80x9chandsetxe2x80x9d which looks much like a telephone but includes a duplex radio link with a base station. The base station is hard wired to a standard telephone line. Communication is established between the base station and the handset either upon initiation of a call by the handset user, or an incoming telephone call received over the telephone line by the base unit. The handset typically includes batteries which are recharged by placing the handset in the base station.
Only a relatively small portion of the radio spectrum has been allocated to cordless telephones and these telephones operate on a selected band of a relatively few channels. The frequency a particular telephone uses is usually made permanent by hardwiring or by setting a switch which may or may not be readily accessible by the user. Typically, the base unit and the handset are permanently set to the same frequency. Because of the small number of channels available, it is possible a person will select the same channel on his cordless telephone as another user, especially in a relative dense urban or suburban area. This results in interference and can lead to unauthorized use of a cordless telephone by allowing unauthorized users to gain access to another user""s telephone. To prevent unauthorized use, it is common to employ a security code in cordless telephone systems.
Numerous systems for providing such security have been developed and typically involve storing an electronic identification code in both the base unit and the mobile units and then checking for corresponding codes prior to establishing a communications link. A simple means for establishing security is to send a tone through the transmitter to the receiver and if the appropriate tone is detected, communication is established. A variety of code storage techniques have been developed including providing the units with hardwired circuitry for generating a code, providing each unit with a removable programmable identification storage xe2x80x9ccode plugxe2x80x9d, or providing each unit with memory circuitry into which a user manually enters a code.
Each of these methods has drawbacks. For example, the use of hard-wired circuitry to generate a code requires each unit to be individually wired in a unique manner greatly increasing manufacturing costs. Code plugs must be uniquely programmed prior to installation and generally only a relatively few user-selected codes are available in order to avoid excessive manufacturing costs. Because relatively few identification codes are available, there is an increased likelihood that other users could accidentally or intentionally select the same codes, thereby compromising the security of the communication system. Also, if a purchaser desires either a new base unit or mobile unit for use in an existing system, it is necessary for either the manufacturer or the purchaser to assure that the unit obtained contains the proper code for allowing communication with other units of the system.
The present invention generates a random identification code and stores the identification code in the internal RAM of the microprocessor of the base unit. The identification code is transmitted to the handset unit by varying the current flow through a coil in the base unit in proportion to the identification code. As the current flows through the coil the magnetic flux density surrounding the coil also varies. A magnetic flux detector in the handset detects the change in flux density and sends this information to a microprocessor in the handset, thus establishing a new identification code.
Thus, matching a specific base unit and a specific mobile unit is no longer done manually, but automatically each time a mobile unit is replaced on the base unit. In addition, code matching is performed frequently because recharging the battery in the handset is done periodically and placing the handset in the base unit automatically triggers the identification code transfer process. A further advantage of the present invention is it is possible to change either the base unit or handset without trying to match existing permanent identification codes in advance.
The utility of this invention is not limited to cordless telephones. Paging systems have a base station and a plurality of pager receivers for receiving signals sent from the base station. These pager receivers have their own identification codes allotted. Upon the generation of a call request to any pager receiver, the base station inserts a corresponding identification code into the paging signal and transmits it. Each time the pager receiver receives a paging signal, it compares the identification code of the paging signal with their own initially stored identification codes for identification. If there is a match, an audible alert is produced, informing the owner of the pager receiver that there is a call. By storing each pager""s code separately in memory when the pager is recharged, the code for each pager can be changed independent of the other pagers or it can be the same for all.
In view of the foregoing it is a general object of the present invention to provide a new and improved electronic system wherein a base station unit communicates with one or more mobile units.
According to the teachings of this invention, a novel identification code transmission system for communications devices of the type having a base station unit and at least one mobile unit is disclosed including: means for generating an identification code in said base unit; means for storing said identification code in said base unit; means for storing said identification code in said mobile unit; and means for transmitting via magnetic coupling said identification code from said base unit to means for detecting the transmitted identification code in said mobile unit and storing it in said means for storing said identification code in said mobile unit.
An identification code transmission system is disclosed wherein said transmission system further includes sensing means for sensing when said mobile unit is proximate to said base unit and wherein said magnetic coupling means comprises a means for measuring Hall effect. It is a further object of this invention to have a telephone communications base unit and a cordless telephone handset.
In one embodiment of the invention there is a base station unit having an identification code generator, an identification code memory in said base unit, and at least one mobile unit with an identification code memory in said mobile unit and a transmitter for sending said identification code from said base unit identification code memory to said identification code memory wherein said transmitter varies the magnetic flux of said mobile unit when the mobile unit is proximate the base unit.
It is an object of this invention to practice a method for transmitting identification codes for electronic message transmission systems of the type having a base unit, with electronic memory, and one or more mobile units, with electronic memory by: selecting an identification code in said base unit; replacing any existing identification code(s) in said base unit memory; and transmitting the identification code from the base unit to the mobile unit by means of magnetic flux. The identification code may be produced by using a random number generator to generate said identification code and a Hall effect transistor may be used to receive said magnetically transmitted identification code.
Various other purposes and advantages of the invention will become clear from its description in the specification that follows. It will be understood that the invention is not limited to the precise embodiment disclosed below and that alternative embodiments and methods will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention as defined in the claims.